Array type ultrasound probe, manufacturing method and driving method of array type ultrasound probe

ABSTRACT

A driving method of an array type ultrasound probe, in which transmission and reception are carried out by changing a voltage load alternatively on the transmission piezoelectric element and the reception piezoelectric element.

This application is a divisional of application Ser. No. 11/811,065filed Jun. 8, 2007 which is based on Japanese Patent Application No.2006-163227 filed on Jun. 13, 2006 Japanese Patent Office, the entirecontent of each of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to an array type ultrasound type probe anda manufacturing method and a driving method of the array type ultrasoundprobe used for medical diagnosis.

An ultrasound diagnosis apparatus is a medical imaging apparatus whichobtains a tomography image of a soft tissue of a biological objectthrough ultrasound pulse reflection method without damages. Theultrasound diagnosis apparatus is compact, inexpensive and safetywithout causing irradiation by X-ray, compared to other medical imagingapparatuses. It is widely used in departments of cardiovascular disease(arteria coronaria of the heart), digestive organs (gastrointestinal),internal medicine (liver, spleen and pancreas), urology (kidney andbladder) and obstetrics and gynecology. Such ultrasound probe used forthe ultrasound medical diagnosis apparatus generally utilizes apiezoelectric effect of a piezoceramic so as to perform transmission andreception of ultrasound with a high sensitivity and a high resolution.In this case, as a vibration mode of the piezoelectric element fortransmission and reception, a single type prove and an array type probein which a plurality of probes are disposed two-dimensionally arepopularly used. Since array type can obtain a fin image, it is popularlyused for the medical image for diagnostic examination On the other hand,since harmonic imaging diagnosis using a harmonic signal can obtain aclear image which conventional B mode diagnosis cannot obtain, it isbecoming a standard diagnosis modality. A harmonic imaging technology isa technology to improve a resolution of a ultrasound image and to form afine image, where the ultrasound probe transmits a fundamental wave (f1)having a certain frequency to an organic object and receives a harmonicwave reflected by the organic object having frequency components, whichare integral multiplication (for example, 2 times, 3 times, 4 times and5 times) of frequency of the aforesaid fundamental wave, and variousimage processing are carried out after the ultrasound diagnosisapparatus converts the reflected wave into an electric signal. Thisharmonic imaging technology is also utilized to extract a diagnosisregion as an image where a contrast is emphasized by dosing anultrasound imaging agent including micro bubbles through an artery. Thereason is that the micro bubbles dosed into the organic object has acharacteristic to reflect the harmonic wave strongly.

It is necessary to improve the image quality of the ultrasound image ofthe diagnosis region using the harmonic imaging technology also for theultrasound diagnosis apparatus using an ultrasound probe in which thevibration elements are disposed two-dimensionally. For this purpose, theultrasound probe in which the vibration elements are arrangedtwo-dimensionally is required to have a frequency characteristic ofbroad band including frequency components of the fundamental wave andthe harmonic wave.

The harmonic imaging has various advantages where a contrast resolutionis improved because of a superior S/N ratio due to a small side lobelevel, a horizontal resolution is improved since a beam width is thindue to a high frequency, multi reflection does not occur because afluctuation of a acoustic pressure is small due to a small acousticpressure at close range, and a diagnosis range can be deeper compared toan ultrasound where a decay beyond a focus is a similar level as thefundamental wave and the fundamental wave has a frequency of theharmonic wave.

As a substantial structure of the array type ultrasound probe for theharmonic imaging, an piezoelectric vibration element where eachvibration element configuring an array is a broad band integrated type.There is generally used a method where the fundamental wave istransmitted in a frequency area of a low frequency side of the broadfrequency band characteristic and the harmonic wave is received in ahigh frequency side of the frequency range. Under this circumstances, inconventional ultrasound probes, a technology to improve a sensitivitydisclosed in Patent document 1 is know. This technology is to improvethe sensitivity. In this technology, the vibration element wheremicroscopic pillar-shaped piezoelectric elements bonded by an organiccompound such as, for example, an epoxy resin, is used as an ultrasoundtransmission-reception element, and each pillar-shaped ceramic isvibrated in longitudinally.

A narrow frequency range ultrasound is used so that a spectrum of theultrasound for transmitting the fundamental wave and a spectrum of theultrasound for the receiving harmonic wave do not overlap each other.However, since the narrow frequency range ultrasound is generally anultrasound pulse signal having a long tail, it negatively affects aresolution in a direction of ultrasound emitting.

As other practical structure of array type ultrasound probe forharmonics imaging, for example, a transmission-reception separation typeprobe where the transmission piezoelectric vibration element and thereception piezoelectric vibration element are separately disposed issuggested, in Patent document 2 and 3.

For example in Patent document 3, to transmit the fundamental wave andto receive the ultrasound including the harmonic wave, it is suggestedthat a first piezoelectric layer configured by a plurality of arrayedpiezoelectric element having a first acoustic impedance to carry outtransmission and reception of the ultrasound having a center frequencyof f1, and a second piezoelectric layer configured by a plurality ofarrayed second piezoelectric elements having a second acoustic impedanceand laid on the fist piezoelectric layer to carry out reception of theultrasound having a center frequency of f2=2×f1 are disposed. However asufficient sensitivity is not yet obtained.

Further, to improve the sensitivity it is being practiced that apiezoelectric ceramic element is laminated to lower an apparentimpedance so that an electrical matching condition with a drivingcircuit is improved, and an electrical field intensity is increased tocreate a large distortion so that the transmission sensitivity isimproved. However, in an laminated structure, though the remittancesensitivity is increased in accordance with number of the laminationlayers, the reception sensitivity is inversely proportional to thenumber of the lamination layers, thus it is not preferable for theharmonic imaging.

[Patent Document 1] Unexamined Japanese Patent Application PublicationNo. 63-252140

[Patent Document 1] Unexamined Japanese Patent Application PublicationNo. 8-187245

[Patent Document 1] Unexamined Japanese Patent Application PublicationNo. 11-276478

To manufacture the composite piezoelectric vibration element, apiezoelectric ceramic is cut by a cutting machine such as dicer to forma pillar-shaped structure, thereafter a cutting groove is filled with anorganic material such as an epoxy resin. Also, in case of the array typeprobe, separation of each channel is done by the cutting machine such asthe dicer.

However, since an transmission-receiving frequency depends on athickness of the piezoelectric ceramic, the pillar-shaped structure or achannel pitch becomes smaller as the frequency becomes higher.Therefore, there were problems that a mechanical strength of the ceramicis deteriorated in accordance with increase of machine work by cuttingmachine such as the dicer and a deterioration of properties due to heatand distortion at machining or breakage cannot be ignored, thus adeterioration of an production yield or deterioration of performance ofthe vibration element or the probe, become easy to be caused. Also, tomanufacture the transmission-reception piezoelectric element capable ofa desired frequency, it is indispensable to grind and polish bothsurfaces and is a factor to rise a production cost. As above, there wereproblems to overcome in the production of the probe using ceramicmaterials.

SUMMARY OF THE INVENTION

In view of the above problems of the aforesaid conventional art, anobject of the present invention is to provide a high sensitive arraytype ultrasound probe using a ceramic material for a transmissionpiezoelectric element and using a high sensitive organic piezoelectricelement material for reception, particularly in case an array typeultrasound probe in which the operations of remitting and receiving theultrasound are separated is utilize.

To solve the above problems, in the array type ultrasound probe of thepresent invention, the transmission and reception piezoelectric elementhaving the laminate structure where the sheet-shaped piezoelectricceramic configuring each channel are laminated in the single layer orthe multi layers, and the sheet shaped piezoelectric element forreception are laminated in a single layer or multi layers to separatetransmission and reception for respective piezoelectric elements, and atthe same time, the piezoelectric element configured by the ceramicmaterial and the organic material is combined to make the probe atransmission reception separate type. Thus the high sensitive ultrasoundprove can be obtained. Further, an organic bonding material is used forcombining and an organic bonding layer is brought, thereby thesensitivity is improved further.

Therefore, the present invention can be achieved by the followingstructures and methods.

(1) A multi-channel array type ultrasound probe disposed at leastone-dimensionally, having: a plurality of sheet-shaped piezoelectricelements as transmission-reception separation type complexpiezoelectric, wherein a material configuring a transmissionpiezoelectric element of the complex type piezoelectric element has anelastic coefficient of 10 Gpa to 100 GPa at 23° C., and a materialconfiguring a reception piezoelectric element of the complex typepiezoelectric element has an elastic coefficient of 10 Gpa to 1 Gpa at23° C.(2) A manufacturing method of the array type ultrasound probe, whereinthe reception piezoelectric element of (1) is formed through evaporationpolymerizing where a monomer species is formed into a thin film at lowtemperature on a supporting substance (substrate) selected frompolyester resin, polycarbonate resin, and cycloolefin polymer resin.(3) A driving method of an array type ultrasound probe, whereintransmission and reception are carried out by changing a voltage loadalternatively on the transmission piezoelectric element and thereception piezoelectric element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a cross-sectional view of an ultrasound prove.

FIG. 1 (b) is a cross-sectional view of an ultrasound prove having anorganic bonding layer.

FIG. 2 (a) is a cross-sectional view of an ultrasound prove where areception piezoelectric element is a laminate layer type.

FIG. 2 (b) is a cross-sectional view of an ultrasound probe having anorganic bonding layer.

FIG. 3 (a) a cross-sectional view of an ultrasound prove where TPE andRPE are laminate layer type.

FIG. 3 (b) a cross-sectional view of an ultrasound prove where TPE andRPE are laminate layer type having an organic bonding layer.

FIG. 4 (a) is a side view where probes are arrange parallel in onedimension.

FIG. 4 (b) is a side view where probes are arrange parallel in twodimensions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following is a description of the preferred embodiments of thisinvention without the present invention being restricted thereto:

The embodiments of this invention are described with reference to FIG. 1to FIG. 4 as follows.

FIG. 1 (a) is a side view of an array type ultrasound probe related tothe embodiment of the present invention. FIG. 1 (b) is a side view of anultrasound probe having organic bonding material layer 13. Also, FIG. 2(a) is a cross-sectional view of a lamination layer type transmissionpiezoelectric element configuring the array type ultrasound probe of thepresent embodiment. FIG. 2 (b) is a side view of an ultrasound probehaving organic bonding material layer 13. FIG. 3 (a) is across-sectional view of an ultrasound prove in which the transmissionpiezoelectric element and the reception piezoelectric elementconfiguring the array type ultrasound probe related to the embodiment ofthe present invention are a laminated layer type. FIG. 3 (b) is a sideview of the ultrasound probe having organic bonding material layer 13.Also, in FIG. 1 (a), FIG. 1 (b), FIG. 2 (a) and FIG. 2 (b), numeral 1represents the ultrasound probe, numeral 2 represents the transmissionpiezoelectric element, numeral 3 represents the reception piezoelectricelement, numeral 4 represents an external electrode to apply voltage tothe transmission piezoelectric element, numeral 5 represents a backingmember, numeral 6 represents a first aligning layer, numeral 8 indicatesan emitting direction of the ultrasound, numeral 9 represents a voltageapply electrode for reception and numeral 13 represents the organicbonding material layer. FIG. 1 (a) and FIG. 2 (a) are figures in whichthe bonding materials are not used and FIG. 1 (b) and FIG. 2 (b) arefigures showing examples using the bonding material where a bondingmaterial layer is created between the electrode and the organicpiezoelectric element when the organic piezoelectric layer is bondedwith the ceramic piezoelectric element through the electrode. In casethe ultrasound probe is configured with a single organic piezoelectricelement, one organic bonding material layer (unillustrated) can beimposed between an electrode bonded with the ceramic material and theother electrode on opposite side. In case of the laminated layer type(unillustrated) configured by a plurality of the organic piezoelectricelements, the bonding material layer can be disposed for each electrode.It is essential to provide the bonding material layer because a portionwhere the ceramic piezoelectric element for transmission and the organicpiezoelectric element are bonded through the electrode is directlyaffected by a voltage effect of transmission. FIG. 4 (a) is a side viewwhere the probes are arrayed one-dimensionally and FIG. 4 (b) is a topview where the probes are arrayed two-dimensionally.

An example of a manufacturing method of the allay type ultrasound proberelated to the embodiment of the present invention is explained withreference to FIG. 1 as follows. First, the transmission piezoelectricelement 2 is produced. As FIG. 1 shows, the transmission receptionseparation type piezoelectric element has a structure where transmissionpiezoelectric element 3 and reception piezoelectric element 2 arelaminated. Transmission piezoelectric element 3 can be a structure wherethin electrode plates and electrode layers are imposed as FIG. 2. Suchstructure can be produced in a way, for example, that the electrode isformed on a piezoelectric ceramic green sheet by printing a platinumpaste, and it is laminated before calcination then calcinatedintegrally. A thickness of the green sheet can be easily made not morethan 100 μm and the thickness of each layer can be set arbitrarily inaccordance with existence or nonexistence of the electrode. Receptionorganic piezoelectric element 3 can be produced in the same manner astransmission piezoelectric element 2 by laminating the organic polymersheet. In this case, a portion of the reception piezoelectric elementcan be formed by laminating only the polymer sheet without printingprocess of the electrode using the platinum paste, and the electrode canbe inserted between the lamination layers as FIG. 3 shows.

For the above lamination and inserting the electrode, the organicbonding material may not use. As a convenient method, a general purposeadhesive can be used. In case the transmission ceramic piezoelectricelement and the reception organic piezoelectric element are joined, useof the organic bonding material is preferred since a bonding strength ofa boundary surface between the electrode imposing the organicpiezoelectric element and the organic piezoelectric element isinsufficient, and separation is likely to occur. As preferred organicbonding materials, the following are exemplified without restricting thematerials thereof.

They are at least one kind of resin selected from PVB, polyolefine, polycycloolefin, Polyacrylate, polyamide, polyimide, polyester, polysulfone.As an existing chemical substance in Chemical Substance Control Law,(6)-708 (CASNo.63148-65-2) (Alkyl(C4)acetalpolyvinylalcohol) is quoted arepresentative example of PVB. As polyamide, there are quoted polyamide6, polyamide 66, polyamide 610, polyamide 612, polyamide MXD6, polyamide11, polyamide 12, polyamide 46 and methoxy-ized polyamide (existingchemical substance (7)-383 etc)(polycondensates ofpolyalkylen(C3)polyamine/polyalkylene(C4)dicarboxylicacid/ure a).polyimide is (7)-2211 (CASNo.611-79-0). As silicone, there are quotedexisting chemical substance (7)-476 polyalkyl(C12)siloxane,

(7)-474 (polyalkyl(C12)siloxane), (7)-477 (polyalkyl(hydrogen)siloxane),

(7)-483 (polyalkyl(C9)alkeny(C4)siloxane), and (7)-485(Polyalsodiumalkyl(C4)siliconate). As epoxy, there are a polyphenoltype, a poly glycidyl amine type, an alcohol type and an ester type. Acycloaliphatic type is particularly preferred and chemical materialnumbers of3-2452(3,(4-epoxycyclohexylmethyl(3,4-epoxy)cyclohexanecalboxylate),3-3453, 4-47(2-(3,4-epoxy)cyclohexyl-5,1-spiro-(3,4-epoxy)cyclohexyl-m-dioxane) and5-1052 (1,3,5-tris-glycidyl-isocyanuricacid) are preferred.

An usage amount of these resins is adequately determined in accordancewith a frequency characteristics and a sensitivity required and is from10 nm to 60 μm and preferably from 20 nm to 30 μg in the thickness.

The resin can be dissolved in solvents such as DMSO, DMF and DME and canbe melt by heating bulks up to a melting temperature to be used withoutusing the solvents.

A preferable usage of the organic bonding material is that the bondingmaterial can be used for any layer in lamination of the element and ause of bonding the transmission piezoelectric element and the receptionpiezoelectric element is preferred. For transmission piezoelectricelement, in case the electrode is already formed by printing orapplying, it is preferred to be used on the reception piezoelectricelement where the electrode is not printed.

In the above lamination layer forming process, joining can be conductedintegrally by bonding transmission piezoelectric element 3 and receptionpiezoelectric element 2 together, where the electrode is printedbeforehand either on either the transmission piezoelectric element or onthe reception piezoelectric element in a state of a ceramic sheet and anorganic thin film sheet respectively. In this case, considering atransmission-reception sensitivity characteristic of the piezoelectricelement material and an input/output impedance of a reception circuit, athickness and a material of each lamination layer structure are selectedto produce transmission piezoelectric element 3 and receptionpiezoelectric element 2. Thus, it is preferred that transmissionpiezoelectric element 3 and reception piezoelectric element 2 can havethe adequately selected impedance respectively. Also, it is possiblethat only transmission piezoelectric element 3 is produced bycalcination through the lamination method of the green sheet and coveredby reception piezoelectric element 2 afterward. Or a structure where asheet is applied and dried in advance then extended through uniaxialextension then laminated and processed, and then is bonded to formgrooves between the probes. A lamination layer type where the sheet isextended by uniaxial extension in advance so that the voltage effect ismaximized and processed by polarization (poling process) then laminatedusing the organic bonding material is particularly preferred.

As the organic piezoelectric sheet, copolymer of vinylidene fluoride andolefin fluoride which is high molecule piezoelectric film having a lowtensile elastic coefficient are particularly preferred. For example,there is a material which can be obtained by increasing a slow coolingspeed of heat treatment process (a process to improve crystalline byapply a heat having a temperature between a ferroelectic-paraelectricphase transition point and a melting point) to about 3° C./minute afterforming the film. Further by perform annealing for several 10 minutes(20-30 minutes) at a temperature of 100° C., the elastic coefficient canbe lowered. Also, Any other methods to lower a tensile elasticcoefficient during the production process can be used.

As of a molecular weight of a polymer raw material, in a high moleculematerial, as the molecular weight increase, an inherent flexibility ofhigh molecule increases and it becomes the piezoelectric film having alower tensile elastic coefficient then a high sensitive piezoelectricsheet can be obtained. As of P (VDF-TrFE) and/or (VDF-TeFE), using ahigh molecule piezoelectric substance of which melt flow rate at 230° C.is not more than 0.02 g/minute and preferably not more than 0.01g/minute, a high molecule piezoelectric film having low tensile elasticcoefficient is realized and a high sensitive piezoelectric sheet can beobtained. The aforesaid VDF means vinylidene fluoride, TrFE indicates 3ethylene fluorides and TeFE indicates tetra fluoro ethylene.

On the other hand, in case 3 ethylene fluorides, perfluoro alkyl vinylether (PFA), perfluoro alkoxy ethylene (PAE), and perfluoro hexaethylene are copolymerized, an electrical-mechanical binding constant(piezoelectric effect) in a thickness direction varies with acopolymerization rate. For example, the copolymerization rate ofvinylidene fluoride in copolymerization is preferred to be 60 mol % to99 mol %, however, it is also depends on usage of the organic bondingmaterial used for laminating the ceramic piezoelectric element and theorganic piezoelectric element, thus an appropriate value varies. Themost preferable range of the aforesaid copolymerization rate is 85 mol %to 99 mol %. A polymer including 85 mol % to 99 mol % of vinylidenefluoride and 1 mol % to 15 mol % of perfluoro alkyl vinyl ether,perfluoro alkoxy ethylene and perfluoro hexa ethylene is particularlypreferred, since it suppresses the fundamental wave of transmission andimproves the reception sensitivity of the harmonic wave in a combinationof transmission ceramic piezoelectric element and reception organicpiezoelectric element. Conventionally, while tetra fluoro ethylene, 3ethylene fluorides, were deemed to be adequate, however in thecomposition element of the present invention perfluoro alkyl vinyl ether(PFA), perfluoro alkoxy ethylene (PAE) and perfluoro hexa ethylene areparticularly preferred.

To obtain the high molecule piezoelectric film, it is preferred thatpoling process is continued until polarity inversion is caused. Thepolarity inversion is caused by applying a poling electric field whichis repeatedly inversed. Forming of such a state of polarity inversiondistribution thoroughly, depends on a temperature. At a roomtemperature, several ten thousands times to several hundred thousandstimes of polarity inversions are required. However, if it is in a hightemperature over 80° C., only several times to several ten times ofpolarity inversions are required. Also, in case of the receptionpiezoelectric element, for thin film forming of the element, coronaprocessing of 1 mW/cm² to 1 kW/cm² under a normal pressure can beperformed.

For the harmonic imaging, the reception piezoelectric element ispreferred to be an organic piezoelectric element having sensitivitycapable of receiving a second-order harmonic wave generated by thefundamental wave or above. To receive the second-order harmonic wave orabove, a resonant frequency of the reception piezoelectric element hasto be high in respect to a frequency of the fundamental wave of thetransmission piezoelectric element. The fundamental wave frequency f1 isgenerally selected to be 2 Hz to 20 MHz, and a n-th order harmonic waveis preferred to be 1.5 times to 10 times of the fundamental wavefrequency. After transmission piezoelectric element 3 and receptionpiezoelectric element are bonded, as FIG. 1 to FIG. 3 show, exteriorelectrode 4 for conducting with the interior electrode of transmissionpiezoelectric element 3 is formed on a sound wave radiation surface oftransmission piezoelectric element 3, on its opposite end surface and ona side surface using a platinum paste, silver paste or silver plating,thus transmission electrode 4, ground electrode 9 and receptionelectrode 10 are formed. Thereafter, polarization process (poling) isimplemented, and after a plurality of unillustrated signal wires areconnected with the electrode to form the element of the array typeprobe, first aligning layer 6, second aligning layer 7 and backingmaterial 5 are joined by bonding method, thereafter cutting groove 6reaching to backing material 5 is formed by a dicer to separate eachchannel element, thus the ultrasound prove 1 is formed.

PZT (lead zirconate titanate) is used often as the material of thetransmission piezoelectric element, however the materials not containinglead is used recently. They are rock crystal, lithium niobate (LiNbO₃),niobic acid tantalic acid potassium [K (Ta, Nb)O₃], barium titanate(BaTiO₃), lithium tantalate (LiTaO₃) and strontium titanate (SrTiO₃)

An acoustic lens (not described in the FIG. 1 to FIG. 3) for conversionof ultrasound can be joined with second aligning layer 7. Also, here,while the aligning layer has a two layer structure, it can be a multilayer structure, a single layer structure or a structure without layerin accordance with a subject of examination. Number of layers ispreferred to be two to three.

A longitudinal elastic coefficient of the piezoelectric element isrepresented by a constant of proportion between stress and distortioni.e. a compression force and degree of distortion within an elasticdeformation area. In the embodiment of the present invention, thetransmission piezoelectric element and the reception piezoelectricelement are separated, transmission output is increased as the elasticcoefficient increases. However, the longitudinal elastic coefficient ofthe transmission piezoelectric element under 23° C. is to be between 10Gpa to 100 Gpa, since the transmission wave shape is distorted and a S/Nis deteriorated then noises increase. By the same reason, the higherlongitudinal elastic coefficient of the reception piezoelectric elementis better, however, since the S/N ration is deteriorated, the elasticcoefficient of the reception piezoelectric element under 23° C. is to bebetween 10 MPa to 1 Gpa.

In manufacturing the reception piezoelectric element of the presentinvention, there are a radical polymerization method where severalmonomers are copolymerized using starting agent, a photo polymerizationmethod using a photo sensitizer and an evaporation depositionpolymerization where a monomer is evaporated in an low presseratmosphere at a low temperature to form a thin film. In the presentinvention, one of the above polymerization methods can be adequatelyselected depending on types of the monomers and relative componentsproportions of the copolymers. As one of embodiments which preferablyoperate the reception piezoelectric element, in case of poly urethane,an evaporating deposit copolymerization method is preferable to be used.As monomers for poly urethane, a general chemical formula can indicateH₂N—R—NH₂ structure. Here, alkyne group, phenylene group, bivalenceheterocycle group and heterocycle group whose R can be substituted by anarbitrary substituent group can be included. Poly urethane can becopolymers of urea derivative and other monomers. As preferable polyrethane, aromatic series poly urethane using 4, and 4′-diaminodiphenylmethane (MDA), 4,4′-diphenylmethane diisocyanate (MDI) arequatred.

In case the reception piezoelectric element is manufactured, as asupporting member (substrate) where evaporated monomer is deposited,glass, resin and silicon wafer can be used arbitrarily and for lowtemperature thin film forming polyethylene phthalate,polyethylenenaphthalate, polyester resin, polycarbonate resin, siliconresin, alkylate resin and cycloolefin resin can be adequately selected.

An operation of the ultrasound probe of the present invention isdescribed with reference to FIG. 3. In FIG. 3, a high voltage plus or aburst signal is supplied from P1 to transmission piezoelectric element 3at time of remitting. In case of a plus echo mode, transmissionpiezoelectric element 3 remits a plus ultrasound 8 towards an object tobe examined in which a resonance vibration of total thickness mode isexcited by a drive plus applied to reception piezoelectric element 2.The ultrasound 8 reflected by the object to be examined goes throughtransmission piezoelectric element 3 and reaches to receptionpiezoelectric element 2 to be converted into an electric signal,thereafter it is propagated through an electrode cable to a receivingcircuit of a main body as an output. As the above, according to theembodiment of the present invention, in the ultrasound probe used for anultrasound diagnosis apparatus, a high sensitive probe can be realizedby configuring the transmission reception separating type high sensitivearray probe with the ceramic material and the organic material.

Further, using the aforesaid ultrasound probe, a high sensitiveultrasound medical diagnosis apparatus can be realized while reducingthe cost with workability of the organic material.

EXAMPLE

The following describes the present invention with reference toembodiments without the present invention being restricted thereto.

In the present embodiment, a prototype of the probe and test results ofperformance and durability were indicated.

Example 1 Manufacturing Array Type Ultrasound Probe 1 to 14

<Manufacturing a Reception Piezoelectric Element Film>

(Manufacturing Film M1)

P (VDF-PFA)(composition mole proportion: VDF/perfluoro alkyl vinylether) film was formed 48 μm in a thickness by flow casting DMF(dimethylformamide) solution. Further crystallization was carried out at140° C. Then electrodes were formed on both surfaces by metalevaporation deposit. For this film, polarization inversion was repeatedat 77° C. by applying 1 Hz alternative voltage (triangle wave) having apeak value of ±940 V.

(Manufacturing Film M2)

P (VDF-PFA)(composition mole proportion: VDF/perfluoro alkyl vinylether=88/12) film was formed 48 μm in a thickness by flow casting DMF(dimethylformamide) solution. Further crystallization was carried out at140° C. Then electrodes were formed on both surfaces by metalevaporation deposit. For this film, polarization inversion was repeatedat 82° C. by applying 3 Hz alternative voltage (triangle wave) having apeak value of ±920 V.

(Manufacturing Film M3)

P (VDF-PFA)(composition mole proportion: VDF/HFPHexafluoropropylene=86/12) film was formed 48 μm in thickness by flowcasting DMF (dimethylformamide) solution. Further crystallization wascarried out at 138° C. Then electrodes were formed on both surfaces bymetal evaporation deposit. For this film, polarization inversion wasrepeated at 86° C. by applying 2 Hz alternative voltage (triangle wave)having a peak value of ±962 V.

(Manufacturing Film M4)

P (VDF-PFA)(composition mole proportion: VDF/HFP(Hexafluoropropylene=86/12) film was solved in DMF (dimethylformamide)solution and carbon nuno tube was further added 3 weight percent thenkneaded by a blender and flow casted into a film having a thickness of48 μm. Then annealing was carried out at 138° C. Thereafter electrodesare formed on both surfaces of it by metal evaporation deposit. For thisfilm, polarization inversion was repeated at 86° C. by applying 2 Hzalternative voltage (triangle wave) having a peak value of ±962 V.

<Manufacturing Transmission Piezoelectric Element>

(Film S1: Titanic Acid Family Piezoelectric Element not Including Lead)

Basic ingredient components of CaCO₃, La₂O₃, Bi₂O₃ and TiO₂, and asub-ingredient component of MnO are prepared. For basic ingredientcomponents, weight was measured so that a final composition becomes(Ca_(0.97)La_(0.03))Bi_(4.01)Ti₄O₁₅. Then, by adding pure water, it ismixed in the pure water using a bowl mill in which zirconia medium iscontained, for 8 hours and then thoroughly dried, thus a powder mix wasobtained. Next, the powder mix obtained was pre-burned for two hours at800° C. to produce a pre-burning product. Then pure water was added tothe product obtained and fine pulverized is carried out in pure waterwith the bowl mill in which zirconia medium is contained and then dried,thus ingredient powder for piezoelectric ceramic was produced. In finepulverization, by changing time and conditions of fine pulverization,the piezoelectric ceramic ingredient powder each having particlediameter of 100 nm was obtained. Each piezoelectric ceramic ingredientpowder having different particle diameters to which 6 weight percent ofpure water was added as a binder, was formed into a plate-shaped interimcompact having thickness of 527 μm. Then after the plate-shaped interimcompact was vacuum packed, it was formed by a press having a pressure of235 Mpa. Next, the compact was burned. Then a final sintered compacthaving a thickness of 520 μm was obtained. Meanwhile, the burningtemperature was 110° C. each. An electric field over 1.5×Ec (MV/m) wasapplied for one minute to carry out the polarization process.

(Film S2: Manufacturing of Piezoelectric Element PZT)

As components of PZT, lead, zirconium and titanium are within theformula of Pb(Zr(_(1-x))Ti_(x))O₃(0.47≦×≦1) were prepared. Here, PZThaving x=O2 was prepared. Each oxidative product was measured and purewater was added. Then it was mixed in pure water with a ball millcontaining zirconia medium for 8 hours and dried thoroughly. Thus apowder mix is obtained. The powder mix obtained is temporarily formedand temporarily burned for two hours at 800° C. in the air to make aninterim sintered object. Next, pure water was added to the interimsintered object and fine pulverization was carried out in the ball millcontaining zirconia medium and then dried. Thus piezoelectric ceramicingredient powder was produced. To each piezoelectric ceramic ingredientpowder having different particle diameters 6 weight percent of purewater was added as a binder, is formed into a plate-shaped interimcompact having thickness of 526 μm through a press froming. Then afterthe plate-shaped interim compact is vacuum packed, it is formed by apress having a pressure of 235 Mpa. Next, the compact was burned and afinal sintered compact having a thickness of 520 μm was obtained.Meanwhile, the burning temperature is 780° C. each. An electric fieldover 1.5×Ec (MV/m) is applied for one minute to carry out thepolarization process.

After manufacturing the above ceramic material and organic piezoelectricelement, an ultrasound probe was manufactured experimentally. Thenfundamental frequency f1 having 7.5 MHz was transmitted and a relativereception sensitivity of reception harmonic wave f2 having 15 MHz wasinvestigated. To obtain the relative reception sensitivity, a soundintensity measuring system Model 1805 (1 to 50 MHz) manufactured bySonora Medical System Inc. was used. Also, as a durability test, 100hours continuous transmission and reception test was carried out on theexperimental probe in a room with a temperature of 60° C. Meanwhile, analigning layer having two layers and a backing layer to be adaptable toa wavelength of the ultrasound were prepared in advance. The results areshown in the table 1.

TABLE 1 Transmission Reception Organic piezoelectric piezoelectricbonding element element mateerial f2 Kind Elastic Kind Elastic Thick-reception Prove of Thickness co- of co- Thickness ness relativeDurability number film (μm) efficient film efficient (μm) Kind (μm)sensitivity test Remarks 1 S2 520 60 GPa S2  60 GPa 520 Non Non 10 8Comp. 2 S2 520 60 GPa S1  75 GPa 520 Non Non 7 5 Comp. 3 S2 520 60 GPaS1  75 GPa 520 PVB 1 9 7 Comp. 4 S2 520 60 GPa S1  75 GPa 520 PVB 1 7 5Comp. 5 S2 520 60 GPa S2  60 GPa 520 PVB 2 11 9 Comp. 6 S2 520 60 GPa M1280 MPa 48 Non Non 26 16 Inv. 7 S2 520 60 GPa M1 280 MPa 48 PVB 1 30 30Inv. 8 S2 520 60 GPa M1 280 MPa 48 Polyimide 1 30 33 Inv. 9 S2 520 60GPa M2 280 MPa 48 Epoxy 1 32 32 Inv. 10 S2 520 60 GPa M2 280 MPa 48Polyimide 1 30 30 Inv. 11 S2 520 60 GPa M3 280 MPa 48 PET 2 30 29 Inv.*The thickness of the ceramic piezoelectric element is adjusted bygrinding Note 1) Symbols of organic bonding materials 1 PVB: poly vinylbutyral((6)-708), 2 polyimide: (7)-2211, 3 epoxy: (3)-3453 4 polyester:poly ethylene terephthalate(PET), 5 Silicone: (7)-476 6 Polysulfone:Existing chemical substance number (7)-1262, 7 Olefine: polypropylene 8polyarylate: condensation product of bisphenol and phthalic acid Note 2)Elastic coefficient indicates longitudinal elastic coefficient as socalled “Young's modulus”, Comp.: Comparative example, Inv.: The presentinvention

Referring to the above table, according to the present invention, therewaas realized a transmission and reception separation type highsensitive ultrasound probe using a multi-channel array type ultrasoundprobe in which a plurality of the proves where the receptionpiezoelectric having a structure in which the sheet-shaped ceramicmaterial element are laminated in single layer or in multi layers andthe reception organic piezoelectric element are combined, are arrangedat least one-dimensionally. Further, using the bonding material layerbetween the organic piezoelectric element and the electrode, thedurability can be improved.

Embodiment 2 Manufacturing of Polyurethane Piezoelectric Element byEvaporation Polymerization

4.4′ diamino diphenylmethane (MDA), 4.4′ diphenylmethane di isocyanato(MDI) were selected as the monomer and evaporation polymerization wascarried out. MDA was placed on a tray in a vacuum camber of 2×10³ Pa andheated at 100° C. then MDI was heated to be a substrate on an upper partof the chamber. On a polyethylene terephthalate resin (PET) having athickness of 200 nm on which aluminum evaporation was applied in athickness of 200 nm beforehand, evaporation was carried out so that thethickness becomes 48 μm. MDA/MDI rate obtained was 1.1. The electrodewas applied by aluminum evaporation coating, and polarization (poling)was carried out for 10 minutes at an electric field of 120 MV/m under atemperature of 212° C.

Using the polyurethane film produces (referred as M5), an examinationwas carried out in the same manner as specimen number 6 in embodiment 1.Here, as the reception piezoelectric element, the aforesaid polyurethanepiezoelectric element was used (specimen number 15). As polarizationprocess corona discharge was carried out (specimen number 16). Thecorona process was carried out at 8 W/cm² at normal temperature.Further, the polyimide bonding material was heat-sealded by 1 μm betweenthe electrode and poly urethane (specimen number 17). Further in thesame manner as specimen number 17 of embodiment 2, a probe was produced.Here, a poly urethane film was evaporated 6 μm in the thickness andaluminum was evaporated as the electrode, then this procedure wasrepeated 8 times to form a polyurethane having seven electrodes of total48 μm in a thickness. After final evaporation of the electrode wascompleted, polarization process was carried out through lead wires fromthe electrodes at 120 MV/m under a temperature of 212° C. for 10 minutes(specimen number 18).

The same evaluation as in embodiment 1 was carried out for the aforesaidspecimen and the results are shown in table 2.

TABLE 2 Transmission Reception Organic piezoelectric piezoelectricbonding element element mateerial f2 Kind Elastic Kind Elastic Thick-reception Prove of Thickness co- of co- Thickness ness relativeDurability number film (μm) efficient film efficient (μm) Kind (μm)sensitivity test Remarks 15 S2 520 60 GPa M5 280 MPa 48 Non Non 27 16Inv. 16 S2 520 60 GPa M5 280 MPa 48 Non Non 28 16 Inv. 17 S2 520 60 GPaM5 280 MPa 48 Polyimide 1 33 33 Inv. 18 S3 521 61 GPa M6 281 MPa 48Polyimide 1 33 33 Inv. *The thickness of the ceramic piezoelectricelement is adjusted by grinding Note 1) Symbols of organic bondingmaterials 1 PVB: poly vinyl butyral ((6)-708), 2 polyimide: (7)-2211, 3epoxy: (3)-3453 4 polyester: poly ethylene terephthalate(PET), 5Silicone: (7)-476 6 Polysulfone: Existing chemical substance number(7)-1262, 7 Olefine: polypropylene 8 polyarylate: condensation productof bisphenol and phthalic acid Note 2) Elastic coefficient indicateslongitudinal elastic coefficient as so called “Young's modulus”, Comp.:Comparative example, Inv.: The present invention

Referring to the table 2, the same preferable performance of theultrasound probe as in case of embodiment 1 was obtained in evaporationpolymerization method also.

According to the above embodiments, in the array type ultrasound probein which the operation of transmission and reception of the ultrasoundis separated, the ceramic material is used for transmissionpiezoelectric element and a high sensitive organic piezoelectricmaterial is used. Thereby a high sensitive array type ultrasound probecan be provided.

1. A driving method of an array type ultrasound probe having a transmission piezoelectric element and a reception piezoelectric element, the method comprising carrying out transmission and reception by changing a voltage load alternatively on the transmission piezoelectric element and the reception piezoelectric element. 